Paul Simon never wrote a song about Kodak Ektachrome, so you’ve probably never heard of it. But you have seen pictures shot on the film: The astronauts brought it to the moon in 1969, and National Geographic photographers have carried it around the globe.

Launched in 1946, Ektachrome evolved from a slightly finicky stock prone to issues with fading into a go-to medium valued for its vibrant colors. Hues skew toward the blue end of the spectrum, creating more-realistic images than the warmer Kodachrome of Simon fame. Both are slide films—meaning they produce full-color pictures right on the film rather than white-is-black/black-is-white negatives. But Ektachrome is easier to handle: While Kodachrome gets its color from dyes in the developing process, Ektachrome contains...